One known type of information storage device is a disk drive device that uses magnetic media to store data and a movable read/write head that is positioned over the media to selectively read from or write to the disk.
Consumers are constantly desiring greater storage capacity for such disk drive devices, as well as faster and more accurate reading and writing operations. Thus, disk drive manufacturers have continued to develop higher capacity disk drives by, for example, increasing the density of the information tracks on the disks by using a narrower track width and/or a narrower track pitch. However, each increase in track density requires that the disk drive device have a corresponding increase in the positional control of the read/write head in order to enable quick and accurate reading and writing operations using the higher density disks. As track density increases, it becomes more and more difficult using known technology to quickly and accurately position the read/write head over the desired information tracks on the storage media. Thus, disk drive manufacturers are constantly seeking ways to improve the positional control of the read/write head in order to take advantage of the continual increases in track density.
One approach that has been effectively used by disk drive manufacturers to improve the positional control of read/write heads for higher density disks is to employ a secondary actuator, known as a micro-actuator, that works in conjunction with a primary actuator to enable quick and accurate positional control for the read/write head. Disk drives that incorporate a micro-actuator are known as dual-stage actuator systems.
Various dual-stage actuator systems have been developed in the past for the purpose of increasing the access speed and fine tuning the position of the read/write head over the desired tracks on high density storage media. Such dual-stage actuator systems typically include a primary voice-coil motor (VCM) actuator and a secondary micro-actuator, such as a PZT element micro-actuator. The VCM actuator is controlled by a servo control system that rotates the actuator arm that supports the read/write head to position the read/write head over the desired information track on the storage media. The PZT element micro-actuator is used in conjunction with the VCM actuator for the purpose of increasing the positioning access speed and fine tuning the exact position of the read/write head over the desired track. Thus, the VCM actuator makes larger adjustments to the position of the read/write head, while the PZT element micro-actuator makes smaller adjustments that fine tune the position of the read/write head relative to the storage media. In conjunction, the VCM actuator and the PZT element micro-actuator enable information to be efficiently and accurately written to and read from high density storage media.
One known type of micro-actuator incorporates PZT elements for causing fine positional adjustments of the read/write head. Such PZT micro-actuators include associated electronics that are operable to excite the PZT elements on the micro-actuator to selectively cause expansion or contraction thereof. The PZT micro-actuator is configured such that expansion or contraction of the PZT elements causes movement of the micro-actuator which, in turn, causes movement of the read/write head. This movement is used to make faster and finer adjustments to the position of the read/write head, as compared to a disk drive unit that uses only a VCM actuator. Exemplary PZT micro-actuators are disclosed in, for example, JP 2002-133803, entitled “Micro-actuator and HGA” and JP 2002-074871,entitled “Head Gimbal Assembly Equipped with Actuator for Fine Position, Disk Drive Equipped with Head Gimbals Assembly, and Manufacture Method for Head Gimbal Assembly.” Other exemplary PZT micro-actuators are also disclosed in, for example, U.S. Pat. Nos. 6,671,131 and 6,700,749.
FIGS. 1 and 2 illustrate a conventional disk drive unit and show a magnetic disk 101 mounted on a spindle motor 102 for spinning the disk 101. A voice coil motor arm 104 carries a head gimbal assembly (HGA) 100 that includes a micro-actuator 105 with a slider 103 incorporating a read/write head. A voice-coil motor (VCM) is provided for controlling the motion of the motor arm 104 and, in turn, controlling the slider 103 to move from track to track across the surface of the disk 101, thereby enabling the read/write head to read data from or write data to the disk 101. In operation, a lift force is generated by the aerodynamic interaction between the slider 103, incorporating the read/write transducer, and the spinning magnetic disk 101. The lift force is opposed by equal and opposite spring forces applied by a suspension of the HGA 100 such that a predetermined flying height above the surface of the spinning disk 101 is maintained over a full radial stroke of the motor arm 104.
FIG. 3 illustrates the head gimbal assembly (HGA) 100 of the conventional disk drive device of FIGS. 1-2 incorporating a dual-stage actuator. However, because of the inherent tolerances of the VCM and the head suspension assembly, the slider 103 cannot achieve quick and fine position control which adversely impacts the ability of the read/write head to accurately read data from and write data to the disk. As a result, a PZT micro-actuator 105, as described above, is provided in order to improve the positional control of the slider and the read/write head. More particularly, the PZT micro-actuator 105 corrects the displacement of the slider 103 on a much smaller scale, as compared to the VCM, in order to compensate for the resonance tolerance of the VCM and/or head suspension assembly. The micro-actuator 105 enables, for example, the use of a smaller recording track pitch, and can increase the “tracks-per-inch” (TPI) value by 50% for the disk drive unit, as well as provide an advantageous reduction in the head seeking and settling time. Thus, the PZT micro-actuator 105 enables the disk drive device to have a significant increase in the surface recording density of the information storage disks used therein.
Referring more particularly to FIGS. 3 and 4, a conventional PZT micro-actuator 105 includes a ceramic U-shaped frame which has two ceramic beams or side arms 107 each having a PZT element thereon. The ceramic beams 107 hold the slider 103 therebetween and displace the slider 103 by movement of the ceramic beams 107. The PZT micro-actuator 105 is physically coupled to a suspension tongue 114 of suspension 113. Three electrical connection balls 109 (gold ball bonding or solder ball bonding, GBB or SBB) are provided to couple the micro-actuator 105 to the suspension traces 110 located at the side of each of the ceramic beams 107. In addition, there are four metal balls 108 (GBB or SBB) for coupling the slider 103 to the traces 110.
FIG. 5 generally shows an exemplary process for assembling the slider 103 with the micro-actuator 105. As illustrated, the slider 103 is partially bonded with the two ceramic beams 107 at two predetermined positions 106 by epoxy 112. This bonding makes the movement of the slider 103 dependent on the movement of the ceramic beams 107 of the micro-actuator 105. A PZT element 116 is attached on each of the ceramic beams 107 of the micro-actuator to enable controlled movement of the slider 103 through excitation of the PZT elements 116. More particularly, when power is supplied through the suspension traces 110, the PZT elements 116 expand or contract to cause the two ceramic beams 107 of the U-shape micro-actuator frame to bend in a common lateral direction, thereby making the slider 103 undergo a lateral translation and move on the track of the disk in order to fine tune the position of the read/write head. In this manner, controlled displacement of slider 103 can be achieved for fine positional tuning.
Referring to FIG. 6, the load beam 160 of the suspension 113 has a dimple 162 formed thereon that engages the suspension tongue 114. A parallel gap 170 is provided between the suspension tongue 114 and the micro-actuator 105 to allow the micro-actuator 105 to smoothly displace the slider 103 when a voltage is input to the PZT elements of the micro-actuator 105. The gap 170 is important for micro-actuator operation and HGA performance.
FIGS. 7 and 8 illustrate a tilt problem with this prior design arrangement. Due to manufacturing issues, the micro-actuator 105 may creep or tilt when the slider is flying on the disk. For example, FIG. 7 illustrates the gap 170 being reduced when the micro-actuator 105 tilts towards the suspension tongue 114, and FIG. 8 illustrates the gap 170 being increased when the micro-actuator 105 tilts away from the suspension tongue 114. A general case scenario is that the head static angle may change, and a worst case scenario is that the micro-actuator tilt may cause engagement between the micro-actuator 105 and the suspension tongue 114. Both of these scenarios will affect micro-actuator performance and may cause slider read/write errors, cause static problems, affect head flying performance, cause damage to the head/disk system, and/or cause the micro-actuator to not work.
Since the above-described design includes a U-shaped ceramic frame, the brittleness or fragileness of the ceramic material effects the shock performance, e.g., not strong enough shock performance. Also, the previous design has difficulty controlling the parallel gap between the micro-actuator and the suspension tongue during manufacture. In addition, the previous design is difficult for small size slider application, and the previous design has difficulty in the slider mounting process because the slider is mounted on inner side surfaces of the two micro-actuator arms.
Thus, there is a need for an improved micro-actuator for use in head gimbal assemblies and disk drive units that does not suffer from the above-mentioned drawbacks.